Voice-over Internet protocol (VoIP) services have been gaining much attention from communication service providers, their customers and potential customers. VoIP is voice delivered on a network using an Internet Protocol. In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). Communication service providers are using VoIP technology to offer end users more cost-effective voice services across the provider's data infrastructure. These services are typically delivered to customers through a broadband access network, such as a digital subscriber line (DSL) access network. VoIP technology may be used as the foundation for new multimedia communication services that may address mobility and cost reduction concerns to customers. VoIP may also optimize the communication service providers' PSTN network costs, such as when used to transport bulk voice traffic over a shared IP data network.
To ensure the quality of communication messages sent using VoIP, VoIP imposes stringent quality of service (QoS) constraints such as on network mouth-to-ear delay, jitter and packet loss. Mouth-to-ear delay is the delay incurred from the moment the speaker utters words until the instant the listener hears them. The mouth-ear-delay for VoIP-based communications should not exceed 150 ms. The end-to-end jitter may be limited to less than 30 ms and packet loss ratio should not exceed more than 0.5%. To achieve such a level of QoS, the communication service provider may have to provision a large amount of network resources, such as bandwidth, to support the VoIP application. Network bandwidth demanded by VoIP traffic may be closely tied to the codec and the packetization delay used by the VoIP codec. To offer such high-quality calls, communication service providers may have to overprovision resources by assuming a worst combination of all possible codec and packetization delay during service provisioning, which can be costly and inefficient.